The concept of a play-in here is, by definition, unnecessarily complicated and, furthermore, punishes the fourth-place teams in divisions where it's already more difficult to land in fourth place, by forcing them into an extra playoff round that the fourth-place teams in easier divisions get to avoid.

The only way for a wild card to make sense would be to allow for the top three teams in, say, both Eastern Divisions to automatically qualify (preserving the importance of divisional standings) and then select the final two playoff spots by awarding Wild Cards to the remaining two teams (from either division) with the most points. It's simple, straightforward, and something done by both baseball and football.
Playoff matchups then are: Division winners against the two wild cards. Two seed against three seed within the division.

1A 4B*
2A 3A
1B 5B*
2B 3B

* Wild Card

This is not what the NFL does, but ok. They want DIVISIONAL play-offs. What happens when the 4B team wins the first 2 rounds and you have the Maple Leafs as the Pacific Champs? Secondly, the conferences are NOT going to be linked the way the divisions are now and how they were in the 80s and 90s. So, in that case this WOULD be linking the conferences.

If they have this wild card it will be simple. the 4th and 5th place teams will play either a play-in game, or maybe a best of 3. Whether it is done for every conference or just the 8-team conferences, I haven't seen. If it is only done for the 8-team conferences since it would be more "fair" that they only have to beat out 3 teams to get into the play-offs.